I had a problem with this one too. I put it down some time ago & just came back to it today. I was stuck in the same place, I think, and then I noticed that there has to be a 5 in either r7c9 or r8c9. Therefore, there could not be a 5 in r4c9 & there would have to be a 5 in r4c1 or r4c3 -- this let me eliminate the possibility of a 5 in r6c1 & left r5c1 & r6c1 as being either 1 or 7 which allowed me to cancel the other 1's & 7's in that block. I then was able to come up with a few more squares solved & then noticed the 6-4-8 trio in r7c1, r8c1, & r8c4 and then ......... etc.
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Mercedes-Benz C216